Vibratory grinding machine



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7 4- 4 Y) N) l r x r p 0 n ATTORNEY June 24, 1969 GOES JR 3,451,171

VIBRATORY GRINDING MACHINE Filed Nov. 29. 1966 Sheet 1? of 2 Mofor FIG. 2

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ATTORNEY United States Patent O 3,451,171 VIBRATORY GRINDING MACHINE Loring Coes, Jr., Princeton, Mass., assignor to Norton Company, Worcester, Mass., a corporation of Massachusetts Filed Nov. 29, 1966, Ser. No. 597,598 Int. Cl. B241) 47/02 U.S. Cl. 5199 8 Claims ABSTRACT OF THE DISCLOSURE A machine for grinding wheels, and particularly to methods and machines for providing intermittent pressure contact between a grinding wheel and a workpiece. In a particular embodiment of the invention, intermittent or vibratory pressure is applied to successive positions on the cutting surface of a grinding wheel in grinding contact with a workpiece by mounting a drive member or a gear having a given number of teeth on the wheel spindle for driving or meshing with a driven member or gear with an unbalanced weight distribution and having a different number of teeth from the number on the driver gear.

BACKGROUND OF THE INVENTION In the prior art grinding methods and machines it has been found that under constant pressure conditions the cutting rate of a grinding wheel decreases with the time of application. The machine operators have developed hand methods for interrupting the constant pressure contact between the grinding wheel and the workpiece in order to offset the decrease in cutting rate.

The simplest method for interrupting the pressure contact is by successively separating the spinning wheel from the workpiece, but this requires the constant attention of the operator. In another method, the workpiece is struck by a hammer to impart a vibration to the workpiece. Vibratory motion has also been induced by striking the grinding wheel with the workpiece but in both of the last two mentioned methods there is the possibility of danger to the operators resulting from the cracking and breaking of the grinding wheels.

DESCRIPTION OF THE INVENTION It is, therefore, an object of the present invention to provide a grinding machine for producing controlled intermittent pressure contact between a spinning grinding wheel and a workpiece.

Another object of the present invention is an improved grinding machine providing controlled vibrations in a grinding wheel.

Other objects of the invention are to provide grinding machines having improved grinding rates.

Still another object of the present invention is an improvement in the quality of surfaces cut by grinding wheels.

Further objects of the invention are reductions in grinding and labor costs.

A particular object of the invention is to impart a frequency of vibration to a grinding wheel in the direction of work feed that differs from the wheel rotational fre quency.

Still another particular object of the invention is to effect a decrease in the length of the continuous path of individual abrasive grains across the workpiece.

Further objects of the invention are the reduction in swarf erosion of the wheel and an increase in the grinding ratio.

Other objects and advantages of the present invention will become apparent upon further study of the specification, claims and the accompanying drawings wherein:

Patented June 24, 1969 FIGURE 1 shows schematically a side view of a grinding wheel after use in the grinding machine shown in FIGURE 5, the wear throughout a portion of the periphery being exaggerated for the sake of clarity;

FIGURE 2 is a perspective view of one kind of grinding machine that makes use of the present invention;

FIGURES 3 and 4 show graphically some of the improved results produced by this invention; and

FIGURE 5 is a side view, partly broken away, showing another type of grinding machine with my invention in it.

The present invention is best explained by reference to FIGURES 1 and 5. The floor mounted grinding machine of FIGURE 5 has a stationary motor 5 operatively connected to pivot and jack shaft 8 and spindle 7 by flexible drives such as belts. The grinding Wheel 10 and a gear wheel 14 which for example has fourteen teeth thereon, are both secured for rotation with spindle 7. A second gear 12 having twelve teeth thereon meshes with and is driven by gear 14. Gear 12 is purposely made to be unbalanced about its axis of rotation and for this purpose an eccentrically positioned weight 13 is aflixed to gear 12.

In operation the wheel is applied to the work with a force 1 and controlled intermittent pressure contact is maintained between the grinding wheel and the work. The intermittent pressure is produced by rotation of the eccentrically weighed gear wheel 12 and as the grinding wheel rotates the region of maximum pressure contact advances at a uniform rate around the periphery of the wheel, preferably in the direction of rotation of the wheel. Before contact between the work and wheel periphery is repeated at any one point on the periphery, the wheel makes a large number of rotations.

The successive points of contact are shown in FIGURE 1 as occurring along radial lines 1, 2, 3, 4, etc., with an angle a defined between the contacts. At the points of contact a higher unit pressure is applied between the wheel and the work without exceeding the available power, regardless of the size of the work. The intermittent contact caused by the relative in and out feed of the wheel decreases the continuous path of individual abrasive grains contacting the workpiece with a resulting reduction in swarf erosion and an increase in the grinding ratio.

It is preferred in the present invention to couple the grinding wheel and vibrator drives so that the ratio of the wheel vibrational frequency to thewheel rotational frequency is slightly greater than one. If this ratio is a small whole number or a simple small fraction, the operation tends to become progressively bumpy and leads to wedging, stalling and usually to breakage of the grinding wheel.

If the spindle gear has N teeth and the unbalanced gear N teeth, then at a rotational speed of w rpm, the vibrational frequency is w N /N cycles per minute. If, as preferred, N N then each successive impact takes place at an angle a=(N -N )360/N degrees in front of the previous impact point.

In the cut-off machine shown in FIGURE 2, the gear 60, driven directly by the motor 15, has sixty teeth while the gear 61 on the wheel spindle in mesh with the gear 60 has sixty-one teeth. The motor 15 drives the unbalanced gear 60 which in turn drives the gear 61 on the wheel spindle while at the same time producing the required vibration. The gears 12, FIGURE 5, and gears 60, FIGURE 2, can be unbalanced either by attaching lead weights 13 in eccentric positions, or by providing the gears with eccentrically positioned holes therethrough.

In the construction shown in FIGURE 2, the motor driven pulley 6 is not mounted directly on the grinding wheel spindle, as shown at 7 in FIGURE 5. As opposed to FIGURE 2, the arrangement of FIGURES has the advantage of not requiring the power of the motor to be transmitted through gears. Although the arrangement of FIGURE 2 is satisfactory for a small or lightweight machine, it is better in a larger heavier machine such as a floor stand grinder, to keep the motor stationary, as shown in FIGURE 5, so that it does not form part of the vibrating system. The grinding wheel is then driven through intermediate double pulley 8 on the pivot axis of the vibrating frame.

In the construction shown in FIGURE 2 where the gears 60 and 61 have sixty and sixty-one teeth respectively, the impact lead angle on is 5.9, as distinguished from 51.4 in FIGURE where the gears 12 and 14 have twelve and fourteen teeth respectively.

With the motor in FIGURE 2 running at a speed of 1500 rpm, the wheel motor assembly vibrates at a frequency of 1525 cycles/minute.

Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The following preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the specification and claims in any way whatsoever.

wheel wear. To further illustrate the comparative data of Table I and the advantages of vibration versus no vibration the curves shown in FIGURES 3 and 4 were plotted. It can be seen in FIGURE 3 that the cutting rate with vibration is about 1 /2 times the conventional normal rate. It can also be seen in FIGURE 4 that this increase in cutting rate is made at no apparent sacrifice in grinding ratio. Cutting costs are, therefore, reduced about /3.

Example 2 A series of cuts were made on 1" diameter C.R. steel using the cut-off machine of Example 1 with the unbalanced gear engaged and disengaged. The same size grinding wheel was used with two different grinding wheel Equals 15.7 inF.

TABLE II Wh. wear Cutting rate Wheel specification Vlb. Time (min.) (in?) G (infl/hr.) Finish A36RO R 20. 4!) 02 1. 74 46. 0 Clear. A36R0 11-30 27. 87 8. 51 1. 84 33. 8 Slight burr and burn. A46TGB9. 16. 57 0. 68 23. 1 57. 0 o. AMSTGBEL 22. 92 0. 65 24. 2 41. 0 Severe burr and burn.

Example I The cut-off machine shown in FIGURE 2 is powered by a /3 horsepower induction motor belted to the wheel spindle with a resulting spindle speed of 1500 r.p.m. With the spindle gear of 61 teeth and the unbalanced gear of 60 teeth, the lead angle is 5.9. The wheel-motor assembly vibrates about its pivot point at a frequency of 1525 cycles per minute.

Cut-off tests were run on the machine, cutting metals and ceramics, with the unbalanced gear 60 engaged and disengaged to show the effects of vibration. The grinding wheels used were cut-off wheels selected from those disclosed in Abrasives and Grinding Wheels, copyright 1954, 1957 and 1958, by Norton Company, Worcester, Mass, 1965 edition.

A series of cuts were made on Nateo Ceramic Tile using a cut-off wheel 8" outside diameter x A thick x 1%" internal diameter, having a specification 37 C 36 MOR-30. The grinding wheel was operated under the following conditions:

Wheel spindle gear teeth 61 Unbalanced gear d0 60 Amount of unbalance gm. cm 366 Vertical force lb 8 Cutting time sec 30 Spindle speed r.p.m 1500 Eight cuts were made with the same wheel, alternating between vibration and no vibration with successive cuts.

The results obtained are shown in Table I.

TABLE I Cutting Surface, Wear Cut rate (infi/ ft./min. (in?) (111. min.)

2, 940 1. 24 O. 458 0. 370 O. 916 2, 890 1. 92 0. 708 0. 368 1. 416 2, 830 1. 37 0. 466 0. 340 0. 932 2, 780 2. 04 O. 733 O. 359 1. 466 2, 705 l. 68 0. 495 O. 294 O. 990 2, 650 2. 48 0. 632 0. 254 1. 264 2, 560 2. 28 O. 525 O. 230 1. 050 2, 470 3. 01 O. 670 0. 222 1. 340

In the above table the grinding ratio G is equal to the volume of the material cut over the volume of the It can be seen that the use of vibration has, in each case, reduced the cutting time by more than 25% at no sacrifice in grinding ratio G. The cutting costs are, therefore, reduced 25%. The use of vibration improved the finish produced in both cases.

It will be understood that this invention is susceptible to modification in order to adapt it to different usages and conditions and, accordingly, it is desired to comprehend such modifications within this invention as may fall within the scope of the appended claims.

I claim:

1. A grinding machine for applying a grinding wheel to a workpiece comprising in combination:

(a) a support frame;

(b) a rotatable grinding wheel journalled in the support frame;

(0) means, including a driven unbalanced member for effecting intermittent successive non-repetitive spaced points of higher pressure wheel contact with the workpiece during rotation of the grinding wheel; and

(d) means for rotating the grinding wheel and driving the means for effecting said intermittent contact.

2. A grinding machine as defined in claim 1 wherein:

(a) the support frame is pivotally mounted relative to the workpiece;

(b) the unbalanced member is rotatably journalled in said frame; and

(c) the means for effecting intermittent contact further includes: means for driving said grinding wheel and said unbalanced member in synchronism to produce said intermittent contact between the wheel and work.

3. A grinding machine as defined in claim 1 wherein the frequency of said intermittent contact is greater than the frequency of rotation of said grinding wheel.

4. The grinding machine of claim 2 wherein said intermittent contact producing means is a gear having a given number of teeth enmeshed with said unbalanced rotating member and said unbalanced member has a different number of teeth than said given number of teeth.

5. The grinding machine of claim 1, further comprising a stationary motor and means connecting said motor and said grinding wheel for rotation.

6. The grinding machine of claim 2, further comprising 5 6 a motor mounted on said frame and means directly cOn- 2,855,733 10/1958 Allison 51-33 X necting said motor and said unbalanced member. 2,989,824 6/ 1961 Gilman 51-99 X 7. The grinding machine of claim 5 wherein the grind- 3,032,931 5/ 1962 Eversole 5133 X ing wheel in turn drives the intermittent contact producing 3,099,902 8/ 1963 Carlson 51-33 means. 5 3,325,946 6/1967 Lange 5133 *8. The grinding machine of claim 6 'Wherein the unbalanced member in turn drives the grinding wheel. ROBERT RIORDON, Primary Examiner- Refel'ellces Cited D. G. KELLY, Assistant Examiner. UNITED STATES PATENTS 2,504,831 4/1950 Griss 51-59 10 2,580,716 1/1952 Balamuth 5159 51134.5

2,695,478 11/ 1954- Comstock 5172 

